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Twice the sum of the digits of n.
1

%I #9 Apr 17 2022 13:09:22

%S 0,2,4,6,8,10,12,14,16,18,2,4,6,8,10,12,14,16,18,20,4,6,8,10,12,14,16,

%T 18,20,22,6,8,10,12,14,16,18,20,22,24,8,10,12,14,16,18,20,22,24,26,10,

%U 12,14,16,18,20,22,24,26,28,12,14,16,18,20,22,24,26,28,30,14,16,18,20,22,24,26

%N Twice the sum of the digits of n.

%C The only n such that a(n) = n are 0 and 18.

%H Erich Friedman, <a href="https://erich-friedman.github.io/numbers.html">What's Special About This Number?</a>

%F a(n) = 2*A007953(n).

%t 2*Total[IntegerDigits[#]]&/@Range[0,80] (* _Harvey P. Dale_, Apr 17 2022 *)

%Y Cf. A007953.

%K nonn,base

%O 0,2

%A _N. J. A. Sloane_, May 24 2010